Bacteria in Nitrogen Cycle Stages

Steps:

• Identify the process as the nitrogen cycle, with 7 stages involving fixation, assimilation, decomposition, and conversion.
• Recall bacteria perform nitrogen fixation (stage 3, symbiotic or free-living), nitrification (stage 5, converting ammonia to nitrates), and denitrification (stage 7, returning N2 to atmosphere).
• Match these to options: only B lists stages 3, 5, and 7.
• Confirm other stages (1,2,4,6) involve abiotic factors, plants, or animals without bacteria.

Why B is correct:

• Nitrogen cycle definitions specify bacteria drive fixation (Rhizobium), nitrification (Nitrosomonas/Nitrobacter), and denitrification (Pseudomonas), corresponding to stages 3, 5, and 7.

Why the others are wrong:

• A includes 1 (abiotic fixation) and 2 (plant uptake), excluding key bacterial denitrification.
• C includes 4 (ammonification, but misses fixation) and 6 (assimilation, non-bacterial).
• D includes 2 (non-bacterial uptake) and 7 (correct), but misses fixation in 3.

Final answer: B